This invention relates to novel thiopeptolides which have high activity as substrates for vertebrate collagenase.
Collagenase is a proteolytic enzyme which acts on the protein collagen. This enzyme was early found in certain clostridia culture filtrates and shown to act specifically on native (undenatured) collagen at near physiological pH. See Mandl, "Collagenase and Elastases," Advances in Enzymology 23, p. 163, Interscience Publishers, New York, 1961. An illustrative example of a collagenase enzyme product obtained from special strains of Clostridium histolyticum is commercially available from Worthington Biochemical Corporation, Freehold, N.J.
Collagenolytic enzymes also have been obtained by tissue and cell culture from a wide range of animal species in which collagen is metabolized under both physiological and pathological conditions. Collagenase enzymes from such cell and tissue culture sources or from tissue extracts are usually obtained in exceedingly small amounts. Consequently, such enzymes are usually available only by laboratory preparation. An illustrative example of such a preparation is a purified collagenase obtained from culture media of tadpole explant as described by Nagai et al., Biochim. Biophys. Acta 263, 564-573 (1972).
The natural substrate collagen constitutes the connective tissue of the body and is the major type of fibrous protein in higher vertebrae, including mammals. In man, approximately one-third of the total protein content is collagen. The ability of collagenase to digest native collagen provides the enzyme with a variety of uses in tissue culture and cell studies including the isolation of tissue collagen and other types of tissue dissociation. Illustratively, achilles-tendon collagen is hydrolyzed by collagenase to peptides with an average chain length of four to five amino acids.
Collagenase also is believed to be associated with the tissue invasion process in tumor angiogenesis, in arthritic conditions such as rheumatoid arthritis, in corneal ulceration and other diseases of connective tissue. It has been suggested that tumor angiogenesis factor (TAF) induces collagenase secretion by blood vessel endothelial cells. See Moscatelli et al., Cell 20, 343 (1980). The ability of TAF to stimulate collagenase production in endothelial cells provides a basis for assay for TAF and anti-TAF. Accordingly, the measurement of collagenase production is a useful diagnostic tool for tissue invasion.
Conventional assays for collagenase generally are based on methodology developed by Mandl et al., J. Clin. Invest. 32, 1323 (1953). According to these assay procedures, collagenase is incubated for an extended period of time at 37.degree. C. with native collagen. The extent of collagen breakdown is then determined using the Moore and Stein colorimetric ninhydrin method, J. Biol. Chem. 176, 367 (1948). Amino acids which are liberated are expressed as micromoles per milligram of collagenase. One unit of enzyme activity equals the amount of collagenase required to solubilize one micromole of leucine equivalents.
Various synthetic substrates also have been developed heretofore as reagents for the quantitative determination of proteolytic enzymes such as thrombin, plasmin, trypsin and collagenase. These substrates generally consist of relatively short chain peptides. Under the action of the appropriate enzyme, a fragment is hydrolytically split off from the substrate with the resulting formation of a split product, the quantity of which can be measured by conventional photometric, spectrophotometric, fluorescence-photometric, and chromatographic methods. The quantity of the split product formed per time unit is a measure for the enzyme activity from which the quantity of enzyme present in a given test sample can be calculated.
The following are examples of two such synthetic collagenase substrates which are commercially available from Peninsula Laboratories, San Carlos, Calif. and Cal-Med, South San Francisco, Calif.: EQU DNP-Pro-Leu-Gly-Ile-Ala-Gly-Arg-NH.sub.2 "
and EQU DNP-Pro-Gln-Gly-Ile-Ala-Gly-Gln-D-Arg-OH,
wherein DNP=Dinitrophenyl.
In copending application Ser. Nos. 336,520, filed April 8, 1982, Ser. No. 450,318, filed Dec. 16, 1982 and Ser. No. 485,762, filed April 18, 1983, now U.S. Pat. Nos. 4,443,367; 4,466,919 and 4,425,428, respectively, assigned to a common assignee with this application, certain peptides and peptolides are disclosed which have substantially greater activity as collagenase substrates than the aforesaid commercially available substrates.
Other examples of peptide substrates for mammalian collagenase and methods of measuring collagenase activity with the substrates are described in U.S. Pat. Nos. 4,138,394 and 4,176,009; Nagai et al., Biochim. Biophys. Acta 445, 521-524 (1976); Masui et al., Biochem. Med. 17, 215-221 (1977); and Gray et al., Biochem. Biophys. Res. Comm. 101(4), 1251-1258 (1981). Further background information on mammalian collagenase also can be had by reference to the treatise "Collagenase in Normal and Pathological Connective Tissues," Woolley and Evanson, Eds., John Wiley & Son, New York, 1980.